1. Field of the Invention
This invention relates in general to underwater communication systems and, in particular, to a system for controlling voice operated transmission and push-to-talk transmission in a diver communication system.
2. Prior Art
Voice operated transmitters (VOX) are not new to electronics technology or even to diver communication systems. However, when applying conventional technology to the underwater environment, there are many problems. Because the diver is wearing a mask, there are very high levels of noise that can "fool" a conventional VOX system into activation. This unwanted activation by non-voice signals is called "false triggering". The tendency of divers to blow directly into the microphone while swimming or working makes voice activation a particularly difficult problem.
When a diver experiences false triggering, one possible approach is to adjust the microphone sensitivity in an attempt to reduce the susceptibility of the system to activation by extraneous noises. This technique is generally unsatisfactory because it requires the diver to make a manual adjustment. A satisfactory adjustment of the microphone sensitivity is cumbersome and difficult to achieve because manual dexterity is limited in the underwater environment where gloves are commonly used. Moreover, the wide range of frequencies and variations in loudness that can cause false triggering may mean that there is no optimum sensitivity. Thus, this technique may result in degraded voice activation because of lowered microphone sensitivity but not necessarily less false triggering.
Some communication systems have employed external switches that enable the diver to disable VOX operation. If the diver is having problems with false triggering, he can switch to a manual push-to-talk (PTT) mode of operation. However, the use of external mechanical switches offers flexibility only at the expense system reliability. One prior system described in U.S. Pat. No. 5,136,555 to Gardos uses a complicated three-position switch for switching between VOX mode and PTT mode. In that system, VOX operation is enabled by pulling the switch outward to a first switch position. PTT reception is enabled by placing the switch in a central or second switch position. An additional depression of the switch to a third or inward position enables PTT transmission.
In general, the harshness and hazards of the underwater environment require a control system which is simple to operate and in which exposure of the equipment to the harsh and hazardous external environment is limited as much as possible. The use of additional or complicated mechanical switches which are exposed to this undersea environment or the use of diver-operated adjustments increases the possibility of malfunctions and presents additional undesirable demands on the attention of the diver.